Revealing the Charge Storage Mechanism in Porous Carbon to Achieve Efficient K Ion Storage

Constructing a porous structure is considered an appealing strategy to improve the electrochemical properties of carbon anodes for potassium-ion batteries (PIBs). Nevertheless, the correlation between electrochemical K-storage performance and pore structure has not been well elucidated, which hinders the development of high-performance carbon anodes. Herein, various porous carbons are synthesized with porosity structures ranging from micropores to micro/mesopores and mesopores, and systematic investigations are conducted to establish a relationship between pore characteristics and K-storage performance. It is found that micropores fail to afford accessible active sites for K ion storage, whereas mesopores can provide abundant surface adsorption sites, and the enlarged interlayer spacing facilitates the intercalation process, thus resulting in significantly improved K-storage performances. Consequently, PCa electrode with a prominent mesoporous structure achieves the highest reversible capacity of 421.7 mAh g-1 and an excellent rate capability of 191.8 mAh g-1 at 5 C. Furthermore, the assembled potassium-ion hybrid capacitor realizes an impressive energy density of 151.7 Wh kg-1 at a power density of 398 W kg-1. The proposed work not only deepens the understanding of potassium storage in carbon materials with distinctive porosities but also paves a path toward developing high-performance anodes for PIBs with customized energy storage capabilities.

Boundary-Rich Carbon-Based Electrocatalysts with Manganese(II)-Coordinated Active Environment for Selective Synthesis of Hydrogen Peroxide

Coordinated manganese (Mn) electrocatalysts owing to their electronic structure flexibility, non-toxic and earth abundant features are promising for electrocatalytic reactions. However, achieving selective hydrogen peroxide (H2 O2 ) production through two electron oxygen reduction (2e-ORR) is a challenge on Mn-centered catalysts. Targeting this goal, we report on the creation of a secondary Mn(II)-coordinated active environment with reactant enrichment effect on boundary-rich porous carbon-based electrocatalysts, which facilitates the selective and rapid synthesis of H2 O2 through 2e-ORR. The catalysts exhibit nearly 100 % Faradaic efficiency and H2 O2 productivity up to 15.1 mol gcat -1  h-1 at 0.1 V versus reversible hydrogen electrode, representing the record high activity for Mn-based electrocatalyst in H2 O2 electrosynthesis. Mechanistic studies reveal that the epoxide and hydroxyl groups surrounding Mn(II) centers improve spin state by modifying electronic properties and charge transfer, thus tailoring the adsorption strength of *OOH intermediate. Multiscale simulations reveal that the high-curvature boundaries facilitate oxygen (O2 ) adsorption and result in local O2 enrichment due to the enhanced interaction between carbon surface and O2 . These merits together ensure the efficient formation of H2 O2 with high local concentration, which can directly boost the tandem reaction of hydrolysis of benzonitrile to benzamide with nearly 100 % conversion rate and exclusive benzamide selectivity.

CO2 Adsorption on Pore-Engineered Carbons Derived from Jute Sticks

CO2 capture is a practical approach to mitigating the impacts of global warming. Adsorption-based carbon capture is a clean and potentially energy-efficient method whose performance greatly depends on adsorbent design. In this study, we explored the use of jute-derived carbon as a high-performance adsorbent for CO2 capture. The carbons were produced by pyrolyzing powdered jute sticks with NaHCO3 as an activating agent at 500-700 °C. Impressive adsorption capacities of up to 2.5 mmol ⋅ g-1 and CO2 /N2 selectivities of up to 54 were achieved by adjusting the pore size distribution and surface functionalization. Based on the isotherm results, the working capacities, regenerabilities, and potentials for CO2 separation were determined for a practical vacuum swing adsorption process. The adsorbent materials were characterized by XRD, FTIR, Raman, FESEM and N2 sorption at 77 K. This study provides a general approach for designing adsorbents for various gas-separation applications.

Design and Synthesis of N-Doped Porous Carbons for the Selective Carbon Dioxide Capture under Humid Flue Gas Conditions

The design of novel porous solid sorbents for carbon dioxide capture is critical in developing carbon capture and storage technology (CCS). We have synthesized a series of nitrogen-rich porous organic polymers (POPs) from crosslinking melamine and pyrrole monomers. The final polymer's nitrogen content was tuned by varying the melamine ratio compared to pyrrole. The resulting polymers were then pyrolyzed at 700 °C and 900 °C to produce high surface area nitrogen-doped porous carbons (NPCs) with different N/C ratios. The resulting NPCs showed good BET surface areas reaching 900 m² g^-1. Owing to the nitrogen-enriched skeleton and the micropore nature of the prepared NPCs, they exhibited CO₂ uptake capacities as high as 60 cm³ g^-1 at 273 K and 1 bar with significant CO₂/N₂ selectivity. The materials showed excellent and stable performance over five adsorption/desorption cycles in the dynamic separation of the ternary mixture of N₂/CO₂/H₂O. The method developed in this work and the synthesized NPCs' performance towards CO₂ capture highlight the unique properties of POPs as precursors for synthesizing nitrogen-doped porous carbons with a high nitrogen content and high yield.

Heteroatom-Enhanced Porous Carbon Materials Based on Polybenzoxazine for Supercapacitor Electrodes and CO2 Capture

Through a solution method utilizing benzoxazine chemistry, heteroatoms containing porous carbons (HCPCs) were synthesized from melamine, eugenol and formaldehyde, followed by carbonization in a nitrogen atmosphere and chemical activation with KOH at three different activation temperatures, 700, 800 and 900 °C. The introduction of melamine and eugenol to the monomer produced structurally bonded nitrogen and oxygen in porous carbons. Changing the calcination temperature can alter the doping level of heteroatoms and the particle size. These carbon materials exhibit large pore size distributions, tunable pore structure, high nitrogen and oxygen contents and high surface areas, which make them suitable for use as electrode materials in supercapacitors. As a result of activating at 800 °C, the sample HCPC-800 exhibits a high specific surface area of 984 m²/g, high oxygen and nitrogen content (3.64-6.26 wt.% and 10.61-13.65 wt.%), hierarchical pore structure, high degree of graphitization and good electrical conductivity. An outstanding rate capability is also demonstrated, as well as incredible longevity, retaining the capacitance up to 83% even after 5000 cycles in a solution containing 1 M H₂SO₄. Moreover, the activated porous carbon containing nitrogen exhibits a CO₂ adsorption capacity of 3.6 and 3.5 mmol/g at 25 °C and 0 °C, respectively, which corresponds to equilibrium pressures of 1 bar.

Carbon Surface-Influenced Heterogeneity of Ni and Co Catalytic Sites as a Factor Affecting the Efficiency of Oxygen Reduction Reaction

Highly porous carbon black and micro/mesoporous activated carbon were impregnated with cobalt and nickel nitrates, followed by heat treatment at 850 °C in nitrogen. Detailed information about chemistry and porosity was obtained using XPS, XRD, TEM/EDX, and nitrogen adsorption. The samples were used as ORR catalysts. Marked differences in the performance were found depending on the type of carbon. Differences in surface chemistry and porosity affected the chemistry of the deposited metal species that governed the O₂ reduction efficiency along with other features of the carbon supports, including electrical conductivity and porosity. While dissociating surface acidic groups promoted the high dispersion of small metal species, carbon reactivity with oxygen and acidity limited the formation of the most catalytically active Co₃O₄. Formation of Co₃O₄ on the highly conductive carbon black resulted in an excellent performance with four electrons transferred and a current density higher than that on Pt/C. When Co₃O₄ was not formed in a sufficient quantity, nickel metal nanoparticles promoted ORR on the Ni/Co-containing samples. The activity was also significantly enhanced by small pores that increased the ORR efficiency by strongly adsorbing oxygen, which led to its bond splitting, followed by the acceptance of four electrons.

Machine Learning in the Development of Adsorbents for Clean Energy Application and Greenhouse Gas Capture

Addressing climate change challenges by reducing greenhouse gas levels requires innovative adsorbent materials for clean energy applications. Recent progress in machine learning has stimulated technological breakthroughs in the discovery, design, and deployment of materials with potential for high-performance and low-cost clean energy applications. This review summarizes basic machine learning methods-data collection, featurization, model generation, and model evaluation-and reviews their use in the development of robust adsorbent materials. Key case studies are provided where these methods are used to accelerate adsorbent materials design and discovery, optimize synthesis conditions, and understand complex feature-property relationships. The review provides a concise resource for researchers wishing to use machine learning methods to rapidly develop effective adsorbent materials with a positive impact on the environment.

All-Carbon Monolithic Composites from Carbon Foam and Hierarchical Porous Carbon for Energy Storage

We designed high-volumetric-energy-density supercapacitors from monolithic composites composed of self-standing carbon foam (CF) as the conducting matrix and embedded hierarchically organized porous carbon (PICK) as the active material. Using multiprobe scanning tunneling microscopy at selected areas, we were able to disentangle morphology-dependent contributions of the heterogeneous composite to the overall conductivity. Adding PICK is found to enhance the conductivity of the monoliths by providing additional links for the CF network, enabling high and stable performance. The resulting all-carbon CF-PICK composites were used as self-standing electrodes for symmetric supercapacitors without the need for a binder, additional conducting additive, metals as a current collector, or casting/drying steps. Supercapacitors achieved a capacitance of 181 F g^-1 based on the entire mass of the monolithic electrode as well as an outstanding rate capability. Our symmetrical supercapacitors also delivered a record volumetric energy density of 19.4 mW h cm^-3 when using aqueous electrolytes. Excellent cycling stability with almost quantitative retention of capacitance was found after 10,000 cycles in 6.0 M KOH as the electrolyte. Furthermore, charge-discharge testing at different currents demonstrated the fast charge-discharge capability of this material system that meets the requirements for practical applications.

Beyond the Selectivity-Capacity Trade-Off: Ultrathin Carbon Nanoplates with Easily Accessible Ultramicropores for High-Efficiency Propylene/Propane Separation

Rapid and highly efficient C₃H₆/C₃H₈ separation over porous carbons is seriously hindered by the trade-off effect between adsorption capacity and selectivity. Here, we report a new type of porous carbon nanoplate (CNP) featuring an ultrathin thickness of around 8 nm and easily accessible ultramicropores (approximately 5.0 Å). The ultrathin nature of the material allows a high accessibility of gas molecules into the interior transport channels, and ultramicropores magnify the difference in diffusion behavior between C₃H₆ and C₃H₈ molecules, together ensuring a remarkable C₃H₆/C₃H₈ separation performance. The CNPs show a high and steady C₃H₆ capacity of up to 3.03 mmol g^-1 at 298 K during consecutive dynamic cycles, which is superior to that of the state-of-the-art porous carbons and even porous crystalline materials. In particular, the CNPs show a rapid gas diffusivity, which is 1000 times higher than that of conventional activated carbons. This research provides a promising design principle for addressing the selectivity-capacity trade-off for other types of adsorbent materials.

A Top-Down Templating Strategy toward Functional Porous Carbons

Nanostructured carbon materials with high porosity and desired chemical functionalities are of immense interest because of their wide application potentials in catalysis, environment, and energy storage. Herein, a top-down templating strategy is presented for the facile synthesis of functional porous carbons, based on the direct carbonization of diverse organic precursors with commercially available metal oxide powders. During the carbonization, the metal oxide powders can evolve into nanoparticles that serve as in situ templates to introduce nanopores in carbons. The porosity and heteroatom doping of the prepared carbon materials can be engineered by varying the organic precursors and/or the metal oxides. It is further demonstrated that the top-down templating strategy is applicable to prepare carbon-based single-atom catalysts with iron-nitrogen sites, which exhibit a high power density of 545 mW cm^-2 in a H₂ -air proton exchange membrane fuel cell.

Enzymatic Hydrolysis Lignin-Derived Porous Carbons through Ammonia Activation: Activation Mechanism and Charge Storage Mechanism

The low energy density and low cost performance of electrochemical capacitors (ECs) are the principal factors that limit the wide applications of ECs. In this work, we used enzymatic hydrolysis lignin as the carbon source and an ammonia activation methodology to prepare nitrogen-doped lignin-derived porous carbon (NLPC) electrode materials with high specific surface areas. We elucidated the free radical mechanism of ammonia activation and the relationship between nitrogen doping configurations, doping levels, and preparation temperatures. Furthermore, we assembled NLPC∥NLPC symmetric ECs and NLPC∥Zn asymmetric ECs using aqueous sulfate electrolytes. Compared with the ECs using KOH aqueous electrolyte, the energy densities of NLPC∥NLPC and NLPC∥Zn ECs were significantly improved. The divergence of charge storage characteristics in KOH, Na₂SO₄, and ZnSO₄ electrolytes were compared by analyzing their area surface capacitance. This work provides a strategy for the sustainable preparation of lignin-derived porous carbons toward ECs with high energy densities.

High Mass Loading Asymmetric Micro-supercapacitors with Ultrahigh Areal Energy and Power Density

High mass loading asymmetric micro-supercapacitors (MSCs) are key components for the development of high-performance energy and power supply systems. Here, a concept for achieving high mass loading electrodes is presented and applied to high mass loading micro-supercapacitors with ultrahigh areal energy and power density. The positive electrode is made from porous carbon with birnessite coverage and multiwalled carbon nanotubes (CNTs) as conducting additives (PIC-CNTs-MnO₂). The negative electrode is prepared from hierarchically porous active carbon mixed with CNTs (PICK-CNTs). Both positive and negative electrode materials are tailored to ensure a high content of macro- and mesopores. MSCs with an optimized mass loading of 13.9 mg·cm^-2 (maximum: 23.6 mg·cm^-2) provide an ultrahigh areal capacitance of 1.13 F·cm^-2 (volumetric capacitance: 22.6 F·cm^-3), an outstanding energy of 627.8 μWh·cm^-2, and a maximum power density of 64 mW·cm^-2. About 85% of the initial capacitance remained after 5000 cycles. Moreover, shunt and tandem device testing confirmed a high uniformity of these MSCs, meeting the requirements of adjustable output currents and voltages in microchips.

Tunable Nitrogen-Doping of Sulfur Host Nanostructures for Stable and Shuttle-Free Room-Temperature Sodium-Sulfur Batteries

Room-temperature sodium-sulfur batteries have potential in stationary applications, but challenges such as loss of active sulfur and low electrical conductivity must be solved. Nitrogen-doped nanocarbon host cathodes have been employed in metal-sulfur batteries: polar interactions mitigate the loss of sulfur, while the conductive nanostructure addresses the low conductivity. Nevertheless, these two properties run contrary to each other as greater nitrogen-doping of nanocarbon hosts is associated with lower conductivity. Herein, we investigate the polarity-conductivity dilemma to determine which of these properties have the stronger influence on cycling performance. Lower carbonization temperatures produce more pyridinic nitrogen and pyrrolic nitrogen, which from density functional theory calculations preferentially bind discharge products (Na₂S and short-chain polysulfides). Despite its lower conductivity, the highly doped composite showed better Coulombic efficiency and stability, retaining a high capacity of 980 mAh g_(S)^-1 after 800 cycles. Our findings represent a paradigm shift where nitrogen-doping should be prioritized in designing shuttle-free, long-life sodium-sulfur batteries.

Reversing the Irreversible: Thermodynamic Stabilization of LiAlH4 Nanoconfined Within a Nitrogen-Doped Carbon Host

A general problem when designing functional nanomaterials for energy storage is the lack of control over the stability and reactivity of metastable phases. Using the high-capacity hydrogen storage candidate LiAlH₄ as an exemplar, we demonstrate an alternative approach to the thermodynamic stabilization of metastable metal hydrides by coordination to nitrogen binding sites within the nanopores of N-doped CMK-3 carbon (NCMK-3). The resulting LiAlH₄@NCMK-3 material releases H₂ at temperatures as low as 126 °C with full decomposition below 240 °C, bypassing the usual Li₃AlH₆ intermediate observed in bulk. Moreover, >80% of LiAlH₄ can be regenerated under 100 MPa H₂, a feat previously thought to be impossible. Nitrogen sites are critical to these improvements, as no reversibility is observed with undoped CMK-3. Density functional theory predicts a drastically reduced Al-H bond dissociation energy and supports the observed change in the reaction pathway. The calculations also provide a rationale for the solid-state reversibility, which derives from the combined effects of nanoconfinement, Li adatom formation, and charge redistribution between the metal hydride and the host.

Template-Free Formation of Regular Macroporosity in Carbon Materials Made from a Folded Polymer Precursor

Porous carbon materials attract great interest in a wide range of applications such as batteries, fuel cells, and membranes, due to their large surface area, structural and compositional tunability, and chemical stability. While micropores are typically obtained when preparing carbon materials by pyrolysis, the fabrication of mesoporous, and especially macroporous carbons is more challenging, yet important for enhancing mass transport. Herein, template-free regular macroporous carbons are prepared from a mixture of unfolded (linear) and folded (single-chain nanoparticles, SCNP) polyvinylpyrrolidone chains. While having the same chemical composition, the different molecular architectures lead to phase separation even before pyrolysis, creating a dense cell architecture, which is retained upon carbonization. Upon increasing the SCNP content, the homogeneity of the pore network increases and the specific surface area is enlarged 3-5-fold, until ideal properties are obtained at 75% SCNP, as observed by high-resolution scanning electron microscopy and N₂ physisorption porosimetry. The materials are further investigated as hydrazine oxidation electrocatalysts, demonstrating the link between the evolving morphology and current density. Importantly, this study demonstrates the role of polymer architecture in macroporosity templating in carbon materials, providing a new approach to develop complex carbon architectures without the need for external templating.

More Sustainable Chemical Activation Strategies for the Production of Porous Carbons

The preparation of porous carbons attracts a great deal of attention given the importance of these materials in many emerging applications, such as hydrogen storage, CO₂ capture, and energy storage in supercapacitors and batteries. In particular, porous carbons produced by applying chemical activation methods are preferred because of the high pore development achieved. However, given the environmental risks associated with conventional activating agents such as KOH, the development of greener chemical activation methodologies is an important objective. This Review summarizes recent progress in the production of porous carbons by using more sustainable strategies based on chemical activation. The use of less-corrosive chemical agents as an alternative to KOH is thoroughly reviewed. In addition, progress achieved to date by using emerging self-activation methodologies applied to organic salts and biomass products is also discussed.

Porous Carbon-Based Supercapacitors Directly Derived from Metal-Organic Frameworks

Numerously different porous carbons have been prepared and used in a wide range of practical applications. Porous carbons are also ideal electrode materials for efficient energy storage devices due to their large surface areas, capacious pore spaces, and superior chemical stability compared to other porous materials. Not only the electrical double-layer capacitance (EDLC)-based charge storage but also the pseudocapacitance driven by various dopants in the carbon matrix plays a significant role in enhancing the electrochemical supercapacitive performance of porous carbons. Since the electrochemical capacitive activities are primarily based on EDLC and further enhanced by pseudocapacitance, high-surface carbons are desirable for these applications. The porosity of carbons plays a crucial role in enhancing the performance as well. We have recently witnessed that metal-organic frameworks (MOFs) could be very effective self-sacrificing templates, or precursors, for new high-surface carbons for supercapacitors, or ultracapacitors. Many MOFs can be self-sacrificing precursors for carbonaceous porous materials in a simple yet effective direct carbonization to produce porous carbons. The constituent metal ions can be either completely removed during the carbonization or transformed into valuable redox-active centers for additional faradaic reactions to enhance the electrochemical performance of carbon electrodes. Some heteroatoms of the bridging ligands and solvate molecules can be easily incorporated into carbon matrices to generate heteroatom-doped carbons with pseudocapacitive behavior and good surface wettability. We categorized these MOF-derived porous carbons into three main types: (i) pure and heteroatom-doped carbons, (ii) metallic nanoparticle-containing carbons, and (iii) carbon-based composites with other carbon-based materials or redox-active metal species. Based on these cases summarized in this review, new MOF-derived porous carbons with much enhanced capacitive performance and stability will be envisioned.

A Role of Activators for Efficient CO2 Affinity on Polyacrylonitrile-Based Porous Carbon Materials

Herein, we investigated polyacrylonitrile (PAN)-based porous activated carbon sorbents as an efficient candidate for CO2 capture. In this research, an easy and an economical method of chemical activation and carbonization was used to generate activated PAN precursor (PAN-C) adsorbents. The influence of various activators including NaOH, KOH, K2CO3, and KNO3 on the textural features of PAN-C and their CO2 adsorption performance under different temperatures was examined. Among the investigated adsorbents, PANC-NaOH and PANC-KOH exhibited high specific surface areas (2,012 and 3,072 m2 g-1), with high microporosity (0.82 and 1.15 cm3 g-1) and large amounts of carbon and nitrogen moieties. The PAN-C activated with NaOH and KOH showed maximum CO2 uptakes of 257 and 246 mg g-1 at 273 K and 163 and 155 mg g-1 at 298 K, 1 bar, respectively, which was much higher as compared to the inactivated PAN-C precursor (8.9 mg g-1 at 273 K and 1 bar). The heat of adsorption (Q st) was in the range 10.81-39.26 kJ mol-1, indicating the physisorption nature of the CO2 adsorption process. The PAN-C-based activated adsorbents demonstrated good regeneration ability over repeated adsorption cycles. The current study offers a facile two-step fabrication method to generate efficient activated porous carbon materials from inexpensive and readily available PAN for use as CO2 adsorbents in environmental applications.

Boosting the Potassium-Ion Storage Performance in Soft Carbon Anodes by the Synergistic Effect of Optimized Molten Salt Medium and N/S Dual-Doping

Soft carbon is attracting tremendous attention as a promising anode material for potassium-ion batteries (PIBs) because of its graphitizable structure and adjustable interlayer distance. Herein, nitrogen/sulfur dual-doped porous soft carbon nanosheets (NSC) have been prepared with coal tar pitch as carbon precursors in an appropriate molten salt medium. The molten salt medium and N/S dual-doping are responsible for the formation of nanosheet-like morphology, abundant microporous channels with a high surface area of 436 m² g^-1, expanded interlamellar spacing of 0.378 nm, and enormous defect-induced active sites. These structural features are crucial for boosting potassium-ion storage performance, endowing the NSC to deliver a high potassiation storage capacity of 359 mAh g^-1 at 100 mA g^-1 and 115 mAh g^-1 at 5.0 A g^-1, and retaining 92.4% capacity retention at 1.0 A g^-1 after 1000 cycles. More importantly, the pre-intercalation of K atom from the molten salts helps improve the initial Coulombic efficiency to 50%, which outperforms those of the recently reported carbon anode materials with large surface areas. The density functional theory calculations further illuminate that the N/S dual-doping can facilitate the adsorption of K-ion in carbon materials and decrease the ion diffusion energy barrier during the solid-state charge migration.

Fishnet-Like, Nitrogen-Doped Carbon Films Directly Anchored on Carbon Cloths as Binder-Free Electrodes for High-Performance Supercapacitor

The low specific capacitance and energy density of carbon electrode has extremely limited the wide application of supercapacitors. For developing a high-performance carbon electrode using a simple and effective method, a fishnet-like, N-doped porous carbon (FNPC) film is prepared by calcining the KOH-activated polyindole precoated on carbon cloths. The FNPC film is tightly anchored on carbon cloths without any binder. The FNPC film with 3.8 at% N content exhibits a fairly high specific capacitance of 416 F g^-1 at 1.0 A g^-1. Moreover, the assembled button-type cell with two FNPC film electrodes shows a high energy density of 16.4 Wh kg^-1, a high power density of 67.4 kW kg^-1, and long-term cyclic stability of 92% of the initial capacitance after 10 000 cycles at 10 A g^-1. The high performances mainly came from the integration of pseudocapacitance and electrical double-layer capacitance behavior, wettability, fishnet-like nanostructure, as well as the low interfacial resistivity. This strategy provides a practical, uncomplicated, and low-cost design of binder-free flexible carbon materials electrode for high-performance supercapacitors.

Defective Porous Carbon Polyhedra Decorated with Copper Nanoparticles for Enhanced NIR-Driven Photothermal Cancer Therapy

Currently, there is tremendous interest in the discovery of new and improved photothermal agents for near-infrared (NIR)-driven cancer therapy. Herein, a series of novel photothermal agents, comprising copper nanoparticles supported on defective porous carbon polyhedra are successfully prepared by heating a Cu-BTC metal-organic framework (MOF) precursor at different temperatures (t) in the range 400-900 °C under an argon atmosphere. The copper nanoparticle size and carbon defect concentration in the obtained products (denoted herein as Cu@CPP-t) increase with synthesis temperature, thus imparting the Cu@CPP-t samples with distinct NIR absorption properties and photothermal heating responses. The Cu@CPP-800 sample shows a remarkable photothermal conversion efficiency of 48.5% under 808 nm laser irradiation, representing one of the highest photothermal efficiencies yet reported for a carbon-based photothermal agent. In vivo experiments conducted with tumor bearing nude Balb/c mice confirm the efficacy of Cu@CPP-800 as a very promising NIR-driven phototherapy agent for cancer treatment. Results encourage the wider use of MOFs as low cost precursors for the synthesis of carbon-supported metal nanoparticle composites for photothermal therapy.

Pore Characteristics for Efficient CO2 Storage in Hydrated Carbons

Development of new approaches for carbon dioxide (CO₂) capture is important in both scientific and technological aspects. One of the emerging methods in CO₂ capture research is based on the use of gas-hydrate crystallization in confined porous media. Pore dimensions and surface functionality of the pores play important roles in the efficiency of CO₂ capture. In this report, we summarize work on several porous carbons (PCs) that differ in pore dimensions that range from supermicropores to mesopores, as well as surfaces ranging from hydrophilic to hydrophobic. Water was imbibed into the PCs, and the CO₂ uptake performance, in dry and hydrated forms, was determined at pressures of up to 54 bar to reveal the influence of pore characteristics on the efficiency of CO₂ capture and storage. The final hydrated carbon materials had H₂O-to-carbon weight ratios of 1.5:1. Upon CO₂ capture, the H₂O/CO₂ molar ratio was found to be as low as 1.8, which indicates a far greater CO₂ capture capacity in hydrated PCs than ordinarily seen in CO₂-hydrate formations, wherein the H₂O/CO₂ ratio is 5.72. Our mechanistic proposal for attainment of such a low H₂O/CO₂ ratio within the PCs is based on the finding that most of the CO₂ is captured in gaseous form within micropores of diameter <2 nm, wherein it is blocked by external CO₂-hydrate formations generated in the larger mesopores. Therefore, to have efficient high-pressure CO₂ capture by this mechanism, it is necessary to have PCs with a wide pore size distribution consisting of both micropores and mesopores. Furthermore, we found that hydrated microporous or supermicroporous PCs do not show any hysteretic CO₂ uptake behavior, which indicates that CO₂ hydrates cannot be formed within micropores of diameter 1-2 nm. Alternatively, mesoporous and macroporous carbons can accommodate higher yields of CO₂ hydrates, which potentially limits the CO₂ uptake capacity in those larger pores to a H₂O/CO₂ ratio of 5.72. We found that high nitrogen content prevents the formation of CO₂ hydrates presumably due to their destabilization and associated increase in system entropy via stronger noncovalent interactions between the nitrogen functional groups and H₂O or CO₂.

Nitrogen-Doped Superporous Activated Carbons as Electrocatalysts for the Oxygen Reduction Reaction

Nitrogen-containing superporous activated carbons were prepared by chemical polymerization of aniline and nitrogen functionalization by organic routes. The resulting N-doped carbon materials were carbonized at high temperatures (600⁻800 °C) in inert atmosphere. X-ray Photoelectron Spectroscopy (XPS) revealed that nitrogen amount ranges from 1 to 4 at.% and the nature of the nitrogen groups depends on the treatment temperature. All samples were assessed as electrocatalysts for the oxygen reduction reaction (ORR) in alkaline solution (0.1 M KOH) in order to understand the role of well-developed microporosity as well as the different nitrogen functionalities on the electrocatalytic performance in ORR. It was observed that nitrogen groups generated at high temperatures were highly selective towards the water formation. Among the investigated samples, polyaniline-derived activated carbon carbonized at 800 °C displayed the best performance (onset potential of 0.88 V versus RHE and an electron transfer number of 3.4), which was attributed to the highest concentration of N⁻C⁻O sites.

Ginger Straw Waste-Derived Porous Carbons as Effective Adsorbents toward Methylene Blue

In this work, ginger straw waste-derived porous carbons, with high adsorption capacity, high adsorption rate, and good reusability for removing the toxic dye of methylene blue from wastewater, were prepared by a facile method under oxygen-limiting conditions. This study opens a new approach for the utilization of ginger straw waste, and the porous materials can be employed as great potential adsorbents for treating dye wastewater.

Scalable Synthesis of Fe/N-Doped Porous Carbon Nanotube Frameworks for Aqueous Zn-Air Batteries

Aqueous Zn-air batteries are emerging to be ideal next-generation energy-storage devices with high safety and high energy/power densities. However, the rational design and fabrication of low-cost, highly efficient, and durable electrocatalysts on the cathode side remain highly desired. Herein, template-assisted, scalable Fe-implanted N-doped porous carbon nanotube networks (Fe-N-CNNs) have been synthesized based on an environmentally friendly template hydroxyapatite nanowires (HAP NWs). Thanks to the hierarchical meso/micropores, high specific surface area, and abundant active sites, the optimized Fe-N-CNNs exhibit excellent oxygen reduction activity. Furthermore, the Zn-air batteries based on the Fe-N-CNNs cathode deliver a high discharge voltage of 1.27 V at a current density of 20 mA cm^-2 and a large peak power density of 202.2 mW cm^-2 . More far-reaching, this HAP-based template strategy opens a new avenue toward the mass production of efficient, cost-effective electrocatalysts, and the Fe-N-CNNs with hollow interiors are expected to extend their other potential uses in energy storage, molecular sieves, adsorbents, and biomedical engineering.

Metal-Nitrogen-doped Porous Carbons Derived from Metal-Containing Ionic Liquids for Oxygen Reduction Reaction

This study describes a self-doping and additive-free strategy for the synthesis of metal-nitrogen-doped porous carbon materials (CMs) via carbonizing well-tailored precursors, metal-containing ionic liquids (M-ILs). The organic skeleton in M-ILs serves as both carbon and nitrogen sources, while metal ions acts as porogen and metallic dopants. A high nitrogen content, appropriate content of metallic species and hierarchical porosity synergistically endow the resultant CMs (MIBA-M-T) as effective electrocatalysts for the oxygen reduction reaction (ORR). MIBA-Fe-900 with a high specific surface area of 1567 m²  g^-1 exhibits an activity similar to that of Pt/C catalyst, a higher tolerance to methanol than Pt/C, and long-term durability. This work supplies a simple and convenient route for the preparation of metal-containing carbon electrocatalysts.

Cobalt Nanoparticles Encapsulated in Porous Carbons Derived from Core-Shell ZIF67@ZIF8 as Efficient Electrocatalysts for Oxygen Evolution Reaction

The synthesis of electrocatalysts consisting of selectively functionalized parts is an effective strategy to prepare nonprecious electrocatalysts with excellent performance for oxygen evolution reaction (OER). Herein, we synthesized core-shell structured ZIF67@ZIF8 and converted it into Co decorated porous carbons (CS-Co/Cs) consisting of the ZIF67 derived uniformly dispersed Co nanoparticles encapsulated in graphitic carbon as cores and the ZIF8 derived porous carbon as shells. Compared to individual ZIF67 derived samples (Co/Cs), the unique structure of CS-Co/Cs leads to the larger surface area and more hydrophilic surface, both of which facilitate the mass transfer, contributing to the enhanced OER performance. The optimized CS-Co/C sample presents the low overpotential of 290 mV to deliver 10 mA cm^-2 toward OER in 1 M KOH, which is among the best of the reported nonprecious OER electrocatalysts. The CS-Co/C exhibits no obvious current attenuation at 1.53 V for 30 000 s, demonstrating its robust stability.

Sustainable Biomaterials: Current Trends, Challenges and Applications

Biomaterials and sustainable resources are two complementary terms supporting the development of new sustainable emerging processes. In this context, many interdisciplinary approaches including biomass waste valorization and proper usage of green technologies, etc., were brought forward to tackle future challenges pertaining to declining fossil resources, energy conservation, and related environmental issues. The implementation of these approaches impels its potential effect on the economy of particular countries and also reduces unnecessary overburden on the environment. This contribution aims to provide an overview of some of the most recent trends, challenges, and applications in the field of biomaterials derived from sustainable resources.